In order to reduce the cost, time and manpower of long distance shipping, the cargo container is commonly used. Such containers are standardized shapes and sizes and usually have standardized handling devices such as standardized grips, hooks, tie downs and so on that allow shippers, handlers, stevedores, longshoreman, truckers and others to handle numerous containers quickly, almost regardless of the actual contents of the containers.
Normally, such containers are built to specifications issued by various authorities: international use of containers built to these specifications is one of the key ingredients of the modern free trade system, for without such standards, fast handling would be almost impossible.
Perhaps the foremost authority for issuance of such standards is the ISO or International Standards Organization, which issues numbered standards directives. For example “ISO 1496/IV” is one standard for cargo containers, “ISO 1161” another standard for the corner locks of such containers and so on. The Association of American Railroads has similar standards on the same topic, for example AAR M-930. These standards most importantly relate to dimension, but also relate to weatherability, strength and other issues.
Shipping of bulk powders can be a surprisingly aggravating proposition, even when such standardized cargo containers are utilized. Firstly, they are collectively amorphous so entirely closed containers are necessary. Powders and dry particulate matter in general tend to behave in a fashion that allows such bulk powders as food products (e.g. Grain, Flour, Sugar, Dextrose, Starch, Cake Mixes, Cocoa, Coffee, Enzymes, Nutrients, Feeds, Pet Foods, Seeds, Spices, et al.) Chemicals, (e.g. Sodium Chloride, Calcium Chloride, Calcium Carbonate, Lime, Urea, polyethylene, polypropylene, polyester, cements, adhesives, compounds, et al.) Minerals, (e.g. Clays, Fuels, Soils, Stone, et al.). However, such bulk dry particulates or powders usually have an angle of repose, even if a small one, that is there is some angle from the horizontal at which a bulk powder or particulate will rest without flowing, unlike true liquids. Thus, shipping containers for bulk powders tend to have non-flat bottoms. In commonly seen schemes, the container may be subdivided into several smaller compartments, each one with its own “chute” section on the bottom surface of the horizontal container. There are, however, disadvantages to such designs.
One disadvantage is that the numerous small chutes normally used decreased cargo capacity of the container. Switching to one large chute on the bottom side of the container would merely exacerbate this problem under the dictates of simple geometry.
Flow problems also arise: the typical dry particulate matter has a degree of friction which tends to impede or even block flow, while the typical container is not arranged so as to permit the easy discharge of such bulk particulate matter. These problems and other problems stem from the fact that there is no large vertical drop possible within a normal container. The typical standardized container is a matter of 8 feet to 9.5 feet in height (roughly 2400 to 2900 millimeters). This cannot be increased without defeating the entire purpose for having standardized cargo containers.
Pockets or irregularities in such containers also cause retention of portions of the bulk cargo, forcing manual cleaning of the container to finish the unloading of the cargo, or even worse, posing the risk of contamination of the next cargo.
Various types of bulk cargo containers are known, and have various defects.
Those made of inherently strong materials such as heavy gauge steel plate are excessively heavy in relation to the cargo to be carried, not to mention excessively expensive to manufacture. But containers having internal frames tend to provide numerous catch basins or pockets requiring manual cleaning as described above. Containers having external frames eliminate this problem at the cost of reducing the cargo capacity of the container by the depth of the framework on all sides (because of course the framework must fit within the dimensional standards of the container and therefore the “external” frame is actually inside the edges of the container envelope, thus forcing the container itself to sit within the frame). Containers have been made of fiber reinforced plastic materials (sheets of somewhat flexible material of great strength) with external frames have been tried with limited success: potentially decreased weight but potentially decreased durability.
Various examples may be considered. U.S. Pat. No. 6,401,983 B1 issued Jun. 11, 2002 to McDonald et al for BULK CARGO CONTAINER is an example of one such. It uses a conventional horizontal container and a conventional vertical flow path: bulk materials are loaded from above through doors 138, 140 and 142 and unloaded from beneath through discharge openings such as 116.
U.S. Pat. No. 6,059,372 issued May 9, 2000 to McDonald et al for HOPPER BOTTOM TRAILER shows much the same thinking at work: a conventionally horizontal container, possibly subdivided into compartments or cells and a conventional top-in and bottom-out flow path for the bulk materials handled.
U.S. Pat. No. 5,960,974 issued Oct. 5, 1999 to Kee et al for INTERMODAL BULK CONTAINER teaches a container vessel of aluminum within a rigid outer frame with hoppers extending out the bottom of the device and domed aluminum sealing the ends. Hoppers within the shell are once again to be filled from the top and emptied from the bottom.
U.S. Pat. No. 5,529,222 issued Jun. 25, 1996 to Toth et al for DRY BULK PRESSURE DIFFERENTIAL CONTAINER WITH EXTERNAL FRAME SUPPORT teaches exactly that, once again in a substantially horizontal mode.
All of these devices attempt to overcome the friction of the bulk cargo they carry in fairly standard ways. One method is to apply pressure to the air or gaseous atmosphere within the container, i.e. blowing into it, so as to aid the “liquification” of the bulk product and speed flow out through bottom hoppers. This method might allow loading from the bottom as well. The result is a great deal of “plumbing” at the bottom of the device which tends to increase cost and time of manufacture. In addition, the handling facilities at which the container loads and unloads must be equipped to provide such an air pressure differential and having suitable couplings to link to the container's “plumbing” system. Another common solution is to provide relatively highly angled (steep) sided hoppers at the bottom of the vessel, once again however simple geometry dictates that this solution reduces the cargo capacity of the container.
It would be greatly desirable to provide a method of gravity feed of the contents of a bulk cargo container and yet achieve good flow, without overly compromising cargo capacity, and while allowing the additional use of the various devices listed above if desired.